The present invention relates generally to color measurement systems, and more specifically to techniques for providing accurate and precise color measurements at a low cost.
Many endeavors, such as the print and graphics arts, require exacting control of color in many steps of their processes. Such control requires accurate and precise color measurements, including reflective measurements for examining printing inks and emissive measurements for calibrating monitors. Unfortunately, accurate and precise color measurements are difficult and have typically required optical instruments such as spectrophotometers, calorimeters, and densitometers, which incorporate expensive optical and electronic components.
High dynamic range is one contributor to measurement difficulty. A light source to be measured may have intensities that vary over many orders of magnitude from one end of the spectrum to the other. This has typically been addressed by digitizing detector signals with many bits of precision in order to properly evaluate subtle differences in color, which has added considerable expense. Further, the overall intensities of different sources may vary over a considerable range, depending on the type of measurement required. This has typically been addressed by providing individual dedicated instruments for the different types of measurement.
Another source of expense is that the optical instruments have typically required a powerful dedicated computer to perform the computations that transform raw digitized signals into values that are meaningful to the user. This problem is compounded when several different optical measurements need to be made, each one requiring a different specific instrument, each with its own dedicated computer.
Further, optical instruments-are often plagued by what is called veiling glare, the problem of light getting into places it doesn't belong. An example of this occurs in a spectrophotometer that uses a type of monochromator known as a diffraction grating. A diffraction grating spatially separates the different spectral bands of an incident light beam so that the energy in a given spectral band can be measured by rotating the grating to bring the desired spectral band onto a detector. Experience has shown that grating imperfections and other sources of scattered light result in a type of crosstalk where, when the grating is oriented so as to direct light of a particular spectral band toward the detector, small amounts of light of other spectral bands also reach the detector. This can compromise the integrity of the measurement. Possible solutions include using expensive optical components to minimize veiling glare, adding a second monochromator to reduce the error, or both.
These are but a few examples of the technical problems that contribute to the high cost of making accurate and precise color measurements. Thus, while recent advances and price reductions in computer hardware and software have brought many of the necessary graphics and publishing resources to the desktop, the costs of optical instruments for managing and controlling color have typically remained out of the price range of all but the largest commercial enterprises.